Various keyhole covering devices have been utilized to protect key-actuated cylinder locks from unwanted access. Many of these guards utilize an access cover which is removed by means of a second lock, thereby creating a double-lock system. All of these covers, however, require complicated mechanisms and a second locking arrangement which may present just as many problems and opportunities for vandalism as the primary lock. For example, a common tactic of vandals is to insert a toothpick into the keyhole of a cylinder lock and break off the end of the toothpick. This often requires an expensive visit from a locksmith to replace the lock entirely or remove the piece of toothpick from the keyhole. Most prior art lock access covers do not protect against toothpick-type vandalism, since the keyhole of the secondary lock which is used to access the primary lock can just as easily be vandalized.
In order to solve this problem, there exists in the art lockable coverplates which do not have a keyhole. These, however, are complicated mechanisms that are expensive and require the use of bulky, difficult to carry, accessing mechanisms.
The closest prior art of which is pertinent to applicant's invention, but which do not anticipate or suggest his invention, are the following U.S. patents: U.S. Pat. No. 3,477,261 to R. Siana; U.S. Pat. No. 4,073,165 to Grundstrom et al; U.S. Pat. No. 4,107,967 to Grabb; and U.S. Pat. No. 4,732,024 to Nagy.